[RadioKid]

Just "OK" will work.

>いいえ - (iie) - No.
not natural

>いいです　 (ii desu) - It's good. It's ok. It's all right.
>いいですよ　 (ii desu yo)
>問題じゃありません (Mondai ja arimasen) - It's not a problem.

these will work well. You can also say "問題ない:MONDAI NAI;no problem" as a casual form.

Also, "大丈夫(です): DAI-JO-BU（DESU);It’s OK!" (add "DESU" for polite form) will work.